An optical head for recording or reproducing information on the information recording surface of an optical disk rotating at a high speed requires a focus control mechanism for correctly focusing the light beam on the information recording surface of the optical disk and a tracking control mechanism for correctly following the track on the information recording surface of the optical disk. Heretofore, there have been known optical heads of such construction as disclosed in:
(1) Japn. Pat. Appl. No. 54-145462 laid open June 6, 1981 as No. 56-68936 PA1 (2) Japn. Pat. Appl. No. 55-149733 laid open May 11, 1982 as No. 57-74839 PA1 (3) T. Musa et al: OPTICAL HEAD FOR DIGITAL AUDIO DISKS, SPIE. VOl. 329 Optical Disk Technology (1982) PA1 (1) a disk in shape, PA1 (2) formed with a void space between the center and the periphery, PA1 (3) provided with spring elements on its plane, the elements being connected with one another, PA1 (4) with the center portion being connected to the supporting or supported member while the peripheral portion is connected to the supported or supporting member respectively.
Such a conventional optical head unit is packaged with an optical path conversion means such as a mirror or a prism for converting the direction of the light beam from parallel to perpendicular to the surface of said optical disk and a mechanism for controlling the focusing. The unit is contained in an outer shell in a manner so as to be movable relative to the direction of the optical path of the light beam, and a track controlling mechanism is interposed between the outer shell and the unit.
The mechanisms for focus and track controlling respectively include an electromagnetic actuator and are capable of high speed and high precision control by means of an electric signal supplied from outside the optical head according to the rotation of the optical disk.
Of the two mechanisms, the track control mechanism performs its function by causing minute mechanical displacement to the unit as a whole which is fairly heavy as it packages said mirror, prism and the like as the optical path converting means and a mechanism for focus control. Such control should be correctly oriented to the direction of the optical path of the light beam. In case any displacement element in the direction other than said direction should occur, the track controlling and the focus controlling would affect each other to impair correct controlling.
The inventors have made elaborate studies and research on the track control mechanism and noted the following phenomenon. Since the conventional mechanisms are structured with an elastic material such as rubber interposed between the unit and the outer shell which contains the unit, it was found that upon mechanically displacing the unit relative to its outer shell, the elastic material would deform in directions other than that of the displacement. As a result, the displacement of the unit would slightly deviate from the direction of the light beam. Thus, attempting to control the track would cause an adverse effect on the focus control and complicate the controlling operations.
Further, optical disk recording equipments with plural disks in multi-layers instead of packaging with a single optical disk have been developed to thereby increase the recording capacity. In this case the optical head would be inserted in the interval of each optical disk in multi-layers and it would be necessary to construct the optical head as thin as possible in the outer configuration so that the space factor in the optical disk recording equipment can be improved.
Moreover, in the conventional equipment, the actuators for the focus control mechanism packaged in the unit are disposed behind the optical path conversion means in cascade. This was defective as the optical head would become thicker as a whole by the thickness of the actuators.